The drive rods of progressive cavity pumps, also known as screw-type pumps, tend to impart torque to the pump during operation. This torque causes both the pump and the tubing string to rotate in a right hand direction, when viewed from the top. Such rotation is detrimental to the pumping operation.
An anchor is known for use with a progressive cavity pump and is described in Canadian Patent no.1,274,470 issued Sep. 25, 1990 to Weber. This anchor has a drag assembly and a slip assembly disposed about a central tubular member though which the well fluids can pass. The drag assembly carries a drag means, such as spring-biased drag blocks or belly-type springs, and is free to rotate relative to the tubular member. The slip assembly is formed about the tubular member in engagement with the drag assembly. The slip assembly houses slip members having casing engaging surfaces, which are driven between a retracted position and an extended engaging position by action of the drag and slip assemblies rotating about the central tubular member and slip members moving over the surface of the tubular member where it is formed as a mandrel.
Another anchor is described in U.S. Pat. No. 5,275,239 issued Jan. 4, 1994 to Obrejanu. This anchor has a slip assembly housing slip members which are formed to engage the casing when the anchor is rotated in a predefined direction.
These anchors are quite complex and require the use of springs to drive the slip members. The springs are subject to failure and displacement which limits the useful life of each of the anchors. Additionally, the slip members of these anchors always extend out past the surface curvature of the slip housing and are subject to wear when they come into contact with the casing wall during anchor placement and retrieval. It is difficult to remove the slips from the housings in these anchors which makes them very difficult to refurbish and/or repair.